[PATCH] sched/psi: Use task->psi_flags to clear in CPU migration

* [PATCH] sched/psi: Use task->psi_flags to clear in CPU migration
@ 2022-09-26  8:19 Chengming Zhou
  2022-09-27 13:39 ` Johannes Weiner
  2022-10-31 10:53 ` [tip: sched/core] " tip-bot2 for Chengming Zhou
  0 siblings, 2 replies; 3+ messages in thread
From: Chengming Zhou @ 2022-09-26  8:19 UTC (permalink / raw)
  To: hannes, surenb, mingo, peterz; +Cc: linux-kernel, Chengming Zhou

The commit d583d360a620 ("psi: Fix psi state corruption when schedule()
races with cgroup move") fixed a race problem by making cgroup_move_task()
use task->psi_flags instead of looking at the scheduler state.

We can extend task->psi_flags usage to CPU migration, which should be
a minor optimization for performance and code simplicity.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 include/linux/sched.h |  3 ---
 kernel/sched/core.c   |  2 +-
 kernel/sched/stats.h  | 22 ++++------------------
 3 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5cdf746988a1..cffce0eaf640 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -890,9 +890,6 @@ struct task_struct {
 	unsigned			sched_reset_on_fork:1;
 	unsigned			sched_contributes_to_load:1;
 	unsigned			sched_migrated:1;
-#ifdef CONFIG_PSI
-	unsigned			sched_psi_wake_requeue:1;
-#endif
 
 	/* Force alignment to the next boundary: */
 	unsigned			:0;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a7fa9802dfde..2d98b9b5185f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2056,7 +2056,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 
 	if (!(flags & ENQUEUE_RESTORE)) {
 		sched_info_enqueue(rq, p);
-		psi_enqueue(p, flags & ENQUEUE_WAKEUP);
+		psi_enqueue(p, (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED));
 	}
 
 	uclamp_rq_inc(rq, p);
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 84a188913cc9..38f3698f5e5b 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -128,11 +128,9 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 	if (p->in_memstall)
 		set |= TSK_MEMSTALL_RUNNING;
 
-	if (!wakeup || p->sched_psi_wake_requeue) {
+	if (!wakeup) {
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
-		if (p->sched_psi_wake_requeue)
-			p->sched_psi_wake_requeue = 0;
 	} else {
 		if (p->in_iowait)
 			clear |= TSK_IOWAIT;
@@ -143,8 +141,6 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 
 static inline void psi_dequeue(struct task_struct *p, bool sleep)
 {
-	int clear = TSK_RUNNING;
-
 	if (static_branch_likely(&psi_disabled))
 		return;
 
@@ -157,10 +153,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
 	if (sleep)
 		return;
 
-	if (p->in_memstall)
-		clear |= (TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
-
-	psi_task_change(p, clear, 0);
+	psi_task_change(p, p->psi_flags, 0);
 }
 
 static inline void psi_ttwu_dequeue(struct task_struct *p)
@@ -172,19 +165,12 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
 	 * deregister its sleep-persistent psi states from the old
 	 * queue, and let psi_enqueue() know it has to requeue.
 	 */
-	if (unlikely(p->in_iowait || p->in_memstall)) {
+	if (unlikely(p->psi_flags)) {
 		struct rq_flags rf;
 		struct rq *rq;
-		int clear = 0;
-
-		if (p->in_iowait)
-			clear |= TSK_IOWAIT;
-		if (p->in_memstall)
-			clear |= TSK_MEMSTALL;
 
 		rq = __task_rq_lock(p, &rf);
-		psi_task_change(p, clear, 0);
-		p->sched_psi_wake_requeue = 1;
+		psi_task_change(p, p->psi_flags, 0);
 		__task_rq_unlock(rq, &rf);
 	}
 }
-- 
2.37.2


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